Antennas play an important role in communication systems and directly affect communication qualities. As wireless technology continues to thrive, multi-band antennas are used to implement higher speed and various types of services.
A multi-band antenna usually includes an array of sub antennas that are generally categorized as low-band antennas and high-band antennas, which can cooperate at different frequency bands, as illustrated in FIG. 1(a).
Due to the structure of multi-band antennas introduced above, coupling effect and parasitic radiation between the low-band antenna(s) and the high-band antenna(s) may greatly impair the performance of multi-band antennas and users' experience. FIG. 1(b) shows radiation pattern of a low-band sub-antenna array of a conventional multi-band antenna, which is abnormal due to the inter-band coupling effect and parasitic radiation.
Current solution to solve this problem is to add parasitic patches, shaped walls, bars, or arches to the multi-band antennas.